1. Field of the Invention
The present invention relates to a controller for multidegree of freedom nonlinear mechanical system such as an articulated manipulator that can be described by a nonlinear equation of motion, in particular, to a controller which enables a control to be accomplished by carrying out nonlinear compensation in an adaptive manner.
2. Description of the Prior Art
As the systems for controlling a multidegree of freedom nonlinear mechanical system there are known exclusively the following two systems. In the first of the two which is shown in FIG. 1, a closed-loop control system is set up for each degree of freedom 12-1, 12-2, . . . , and 12-n, by completely neglecting the nonlinearity or the interference between the degrees of freedom of the multidegree of freedom nonlinear mechanical system 10. Then, the system is controlled linearly by inserting, for example, PID controllers 14-1, 14-2, . . . , and 14-n corresponding to respective closed loops.
In this system, however, it is difficult theoretically, too, to guarantee the stability of the system over the entire range of operation of the multidegree of freedom nonlinear mechanical system 10. That is, the operation of the system will become nonstable in the nonlinear region of operation, though it is stable in the neighborhood of the region of linear operation. In particular, when the mechanical system is put in a high-speed operation, there arises a problem that a deterioration in the control performance is inevitable due to the influences of the nonlinear forces and the interference between the degrees of freedom of the system.
Now, in the other system of control shown in FIG. 2, the parameters for the multidegree of freedom nonlinear mechanical system 10 are fixed to certain values by assuming that they are all known. Then, a nonlinear compensation is provided based on the results of computation of the nonlinear and interferential forces calculated at a nonlinear compensation unit 16 from the knowledge on the position and the velocity of the system.
However, according to this system, a difficulty exists in that all of the parameters for the multidegree of freedom nonlinear mechanical system 10 have to be known. Namely, among the parameters for the mechanical system there are included those that vary with position, velocity, and time such that it is practically impossible to identify them precisely. Therefore, when there occur errors and variations in the parameters, stability of operation by this system becomes also difficult to guarantee, leading to the problem that its control performance is aggravated excessively.